Mermithida

Definition

An order of nematode worms characterized by a stichosome (a column of glandular cells associated with the esophagus) and comprising obligate endoparasites of arthropods, especially insects and arachnids. Members typically emerge from the host body to reproduce in aquatic or moist terrestrial environments, often causing dramatic behavioral or morphological changes in the host.

Etymology

From Mermithidae, the type family, itself derived from Greek mermis (string, cord) with the diminutive suffix.

Example

Mermithid nematodes such as those in the genus Romanomermis infect mosquito larvae, eventually killing the host when the adult worm emerges; in spiders, mermithid infection can cause enlarged abdomens and altered web-building behavior.

Related Terms

• Mermithidae
• stichosome
• Endoparasite
• Parasitoid
• Nematode
• entomopathogenic nematode
• Romanomermis
• Aranimermis

Usage Notes

Mermithida is an order-level taxon; the family Mermithidae contains most familiar species. The stichosome is a key diagnostic feature distinguishing mermithids from other parasitic nematodes. In entomological contexts, mermithids are often discussed as biological control agents or as confounding factors in arthropod population studies, since infected hosts may survive to adulthood but remain sterile. The term is sometimes used more loosely in older literature to refer to the family Mermithidae.